A light-emitting diode (LED) light-emitting device mainly comprises a combination of a phosphor and a LED chip serving as an excitation light source, and can realize various colors of emission light according to the combination.
Specifically, a white LED light-emitting device, which radiates white emission light, comprises a phosphor in combination with a LED chip that emits light in the blue region. For example, the device comprises a phosphor mixture and a LED chip giving off blue light. In practice, a phosphor emitting yellow light, which is complementary to blue light, is often adopted as the phosphor to produce a pseudo-white LED light-emitting device. Further, a three-wavelength white LED device is also developed which comprises a LED chip emitting blue light, a green- or yellow-light emitting phosphor and a red-light emitting phosphor. As an example of the red-light emitting phosphor used in that light-emitting device, K2SiF6:Mn phosphor is known.
Meanwhile, when conventional fluoride phosphors are continuously excited to emit luminescence, the emission intensity generally tends to go down from the initial intensity in course of time. However, if the phosphors are intended to be used in light-emitting devices, the emission intensity preferably changes little. In other words, the emission intensity maintenance ratio is preferred to be high. It is hence required to improve the emission intensity maintenance ratio. For the purpose of meeting that requirement, it is reported that the phosphors are surface-treated with a solution containing a surface-treatment agent, such as, organic amine or ammonium salt, so as to improve durability thereof under conditions of high temperature and high humidity. However, in order that the phosphors can be subjected to the above treatment after they are synthesized, the step of the treatment must be additionally carried out after the synthesizing process of the phosphors. Accordingly, in view of the production cost, it is desired to develop another method. Further, if conventional fluoride phosphors are brought into contact with water, their emission intensity generally tends to deteriorate. It is therefore not preferred to surface-treat the phosphors with a water-containing solution like the above treatment solution after they are synthesized.